At over 14,411 feet high, Mount Rainier dominates the skyline of the southern Puget Sound region. This glacier-clad mountain is a dormant volcano capable of generating large floods and lahars which have historically reached the floors of the lowlands south of the city of Seattle and out to Commencement Bay in the Port of Tacoma, spewing ash from pyroclastic eruptions. The purpose of this chapter is to promote the public health, safety, and general welfare of the residents of Edgewood by providing standards that minimize the loss of life that may occur as a result of volcanic events emanating from Mount Rainier and the Cascade Mountain Range.
(Ord. 17-513 § 3 (Exh. A); Ord. 25-0695, 12/23/2025)
A. 
General. Volcanic hazard areas are areas subject to pyroclastic flows, lava flows, and inundation by debris flows, mudflows, or related flooding resulting from geologic and volcanic events.
B. 
Volcanic Hazard Area Categories. Volcanic hazard areas are areas that have been historically inundated by lahars or other types of debris flow; affected by pyroclastic flows, pyroclastic surges, lava flows, or ballistic projectiles in future eruptions; or are located in other drainages expected to be inundated by a future debris flow. Volcanic hazard areas within the city are classified into the following categories:
1. 
Inundation Zone for Case I Lahars. Areas that could be affected by cohesive lahars that originate as enormous avalanches of weak chemically altered rock from the volcano. Case I lahars can occur with or without eruptive activity. The average reoccurrence rate for Case I lahars on Mount Rainier is about 500 to 1,000 years.
2. 
Inundation Zone for Case II Lahars. Areas that could be affected by relatively large noncohesive lahars, which most commonly are caused by the melting of snow and glacier ice by hot rock fragments during an eruption, but which can also have a noneruptive origin. The average time interval between Case II lahars from Mount Rainier is near the lower end of the 100- to 500-year range, making these flows analogous to the so-called “100-year flood” commonly considered in engineering practice.
C. 
Travel Time Zones. The ability to evacuate people from within a volcanic hazard area correlates to the distance from the source of an event, i.e., those areas closest to the event will have less time to evacuate than those areas farther away from the source of an event. The amount of time that is anticipated for a debris flow, lahar, flood, or avalanche to travel geographically has been classified into travel time zones. The city is within Time Travel Zone C and D identified on the Pierce County Critical Area GIS database, which is based on the Bulletin of Volcanology, Vol. 60, pp. 98-109, titled: An Empirical Method for Estimating Travel Times for Wet Volcanic Mass Flows by T.C. Pierson, 1998. Time Travel Zone C and D are described as follows:
1. 
Time Zone C. Time Zone C is an estimated two-hour travel distance from the source of the event.
2. 
Time Zone D. Time Zone D is an estimated two-hour or greater travel distance from the source of the event.
(Ord. 17-513 § 3 (Exh. A); Ord. 25-0695, 12/23/2025)
A. 
The city’s Critical Areas GIS database provides an indication of where volcanic hazard areas are located within the city. This database utilizes the volcanic hazard areas indicated in the Washington Geological Information Portal as prepared and maintained by the Washington Department of Natural Resources (WDNR), U.S. Department of Interior Geological Survey documents, and the Pierce County Critical Area GIS database.
B. 
The department will complete a review of the volcanic hazard area maps for any development proposal to determine whether the proposed project area for a regulated activity falls within a volcanic hazard area.
C. 
When the department's maps or sources indicate that the proposed project area for a regulated activity is located within a volcanic hazard area, the department shall apply the standards for regulated activities in volcanic hazard areas, as set forth in EMC § 14.70.040.
(Ord. 17-513 § 3 (Exh. A); Ord. 25-0695, 12/23/2025)
The following standards apply within the inundation zones for Case I and II lahars within the city (refer to Table 14.70.040):
Table 14.70.040
Volcanic Hazard Area Standards
Facility/Occupancy List
Case I Lahar Inundation Zone
Case II Lahar Inundation Zone
Bonus Densities(1)
Not Allowed
Not Allowed
Critical Facilities(2)
Requires Reasonable Use Permit
Requires Reasonable Use Permit
Special Occupancies(3)
In Time Travel Zone C - Limited to 1,000-person occupant load.
In Time Travel Zone D - Limited to 5,000-person occupant load.
Other Occupancies
No Limitation
No Limitation
(1) Bonus density as set forth in EMC § 18.90.080, Housing incentives program.
(2) Critical facility as defined in Chapter 14.20 EMC, except sewer collection facilities and any other utilities that are located underground or not likely to cause harm to people or the environment if inundated by a lahar.
(3) Special occupancy structures as defined in Chapter 14.20 EMC.
(Ord. 17-513 § 3 (Exh. A); Ord. 25-0695, 12/23/2025)